Allowed
Caliber conversion information or blueprints
Magazine holders, speed loaders, stripper clips, or moon clips
Manuals or instruction materials about firearms
Non-pneumatic spear guns
Restricted
Accessories and parts for guns such as butt plates, cases, cleaning supplies, dies, grips, holsters, molds, racks, pistol grips, scopes, slings, stocks, storage cases, or trigger guards. The listing must include a description of the type of firearm the accessory or part is for and what it's used for. If it doesn't, the listing may be removed.
Muzzle loader or black powder gun parts or accessories, as long as each item is offered in one listing at a time. (However, having separate listings for items that can be used to build a gun is prohibited.)
The following gun parts and accessories are allowed on the eBay US site only. The seller must be in the US and offer domestic shipping only:
En bloc clips
Barrels
Bolts
Choke tubes
Cylinders
Firing pins
Hammers
Magazines with a capacity to accept 10 rounds or less (high-capacity magazines that can accept more than 10 rounds are not allowed)
Slides
Trigger assemblies"
